I never used a Dh2g but afaik it simulates a single big display for the base system if nothing else works. Might be you have to set a res of 3840x1080 to get what you want.
In general check the dh2g manual that should tell you what to do.

2 issues.. it's TOTALLY FINICKY! OMG.. if I set the wrong setting, or even "Identify Display" with the MBP in Clamshell mode, it'll turn both of my Dell monitor's off..

Anyways.. right now, I can use Clamshell Mode with 2x1920x1080 in mirrored mode, which sucks and is completely useless.. I might as well turn off 1 of my Dell's.

I can enable 1 large desktop which turns out to be like 2054x1024 for some reason.. I can't set the res higher. I can only get this mode when my MB's lid is open.. if I close it, it puts my MBP to sleep.

Ultimately what I'm trying to do, is use my MBP in clamshell mode, with each monitor at 1920x1080 as 1 large desktop. I can't seem to get this done correctly.. I can't even call their support as they closed 2 hours ago. (5PM EST)

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.